Virtual Leased Line Services
7210 SAS M Services Guide Page 143
from T-PE2 to T-PE1. S-PE1 and S-PE2 will effect the spoke SDP cross-connect only when both
directions of the pseudowire have been signaled and matched.
The pseudowire switching TLV is useful in a few situations. First, it allows for troubleshooting of
the path of the pseudowire especially if multiple pseudowire switching points exist between the
two T-PE nodes. Secondly, it helps in loop detection of the T-LDP signaling messages where a
switching point receives back a label mapping message it already relayed. Finally, it can be
inserted in pseudowire status messages when they are sent from a pseudowire switching node
towards a destination PE.
Pseudowire status messages can be generated by the T-PE nodes and/or the S-PE nodes.
Pseudowire status messages received by a switching node are processed and then passed on to the
next hop. An S-PE node appends the optional pseudowire switching TLV, with its system address
added to it, to the FEC in the pseudowire status notification message only if it originated the
message or the message was received with the TLV in it. Otherwise, it means the message was
originated by a T-PE node and the S-PE should process and pass the message without changes
except for the VCID value in the FEC TLV.
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